Fix UIComponent.CleanUp method execution

[YevgeniyShunevych]

Fix the following case of CleanUp method:

public class SomePage : Page<_>
{
	protected override void OnInit()
	{
		base.OnInit();

		IWebElement iframe = Driver.Get(By.XPath(".//iframe[@id='some-id']"));
		Driver.SwitchTo().Frame(iframe);
	}

	protected override void CleanUp()
	{
		base.CleanUp();

		// Exception can be occurred during AtataContext clean-up.
		Driver.SwitchTo().DefaultContent();
	}
}